Method for establishing a route via a communications network

ABSTRACT

Proceeding from a source terminal device a connection setup message is communicated to a network node of the communication network A network node receiving the connection setup message enters the network node address allocated to it in the communication network and forwards the connection setup message to at least one neighboring network node. Upon reception of the connection setup message at a destination terminal device, a confirmation message is returned to the source terminal device on the identified route, whereby a switching information for a following message transmission is stored in the network nodes that have been traversed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed to a method for establishing a routevia a communication network comprising a plurality of network nodesconnected to one another.

2. Description of the Related Art

In communication networks, a distinction is made between connectionlessand connection-oriented communication networks dependent on the topologyof the communication networks. In connectionless communication networks,a signalling phase preceding a message transmission between commterminal devices allocated to the communication network is omitted, acommunication connection between the communication terminal devicesbeing set up in the framework of said signalling phase. In the frameworkof the signalling phase, a layer-3 connection (switching layer) isestablished according to the OSI reference model (Ōpen {overscore(S)}ystems Īnterconnection), i.e. the communication connection betweenthe communication terminal devices is established by section-by-sectionlinking of individual layer-2 connections (security layer) according tothe OSI reference model—also frequently referred to as point-to-pointconnection in the literature.

Connectionless communication networks are, for example, localnetworks—often abbreviated as LAN ({overscore (L)}ocal Ārea {overscore(N)}etwork) in the literature—with a ring or bus architecture. In aconnectionless communication network, a message package to betransmitted is transmitted to each communication terminal deviceallocated to the communication network. The decision as to whichcommunication terminal device further-processes or, discards thereceived message packet is made by the recipient the he message packet.

Similarly, communication services wherein a message transmission ensueswithout setup of a point-to-point communication connection establishedin the framework of a signalling phase are referred to as connectionlessservices. Such connectionless services, however, can only be realizedwithin local networks (LANs) with corresponding network topology.

In the framework of a message communication between two communicationterminal devices allocated to different comm networks, the lack ofsignalling must be compensated by corresponding measures given a networkinterworking. This compensation ensues with what are referred to asrouters, with which a linking of communication networks with differentnetwork topology is realized.

With respect to its critical function, a router realizes the layer 3(switching layer) of the OSI reference model, whereby networks withdifferent topology of the layers 1 (bit transmission layer) and 2(security layer) are physically connected with the assistance of arouter. In order to switch message packets between the networksconnected to a router, the address particulars contained in routinginformation of the message packets—particularly a destination and asource address—are interpreted and evaluated by a control means locatedin the router. As such the router evaluates the layer-3 addressescontained in a message packet to be transmitted and converts these intocorresponding layer-2 addresses. The layer-2 connections (i.e. theconnections to be respectively established between two network nodesarranged in a network) required for a layer-3 connection (i.e. for theterminal device connection between the communication terminal devices)are established on the basis of these layer-2 addresses. Subsequently,the message packets are converted protocol-suited for a transmission andarc transmitted via the layer-2 connections that have been established.

In the framework of a message transmission via an ATM-basedcommunication network (Āsynchronous {overscore (T)}ransfer {overscore(M)}ode), a signalling phase preceding the message transmission betweenis required for setting up a communication connection between twocommunication terminal devices, i.e. an ATM-based communication networkis a connection-oriented communication network.

Before the beginning of the message transmission, connection tables withswitching information composed of a virtual channel identification andof a virtual path identification are established in the pertinent ATMnetwork node in an ATM-based communication network. In the connectiontables, a VCI value is allocated to the virtual channel identificationand a VPI value is allocated to the virtual path identification. Theswitching information entered in the connection tables define how thevirtual paths—or, virtual transmission channels contained in the virtualpaths—of the incoming and outgoing connections at an ATM network nodeare allocated to one another by the signalling, i.e. which input isconnected to which output in switching-oriented terms.

For example, European Published Application EP 0 406 842 A2 discloses acommunication network based on the asynchronous transfer mode, wherebyswitching information in the framework of a signalling phase are enteredin the traversed network nodes of the communication network with aconnection setup message communicated from a source to a destinationcommunication terminal device and a confirmation message subsequentlycommunicated from the destination to the source communication terminaldevice.

In the cell-based data transmission method known as asynchronoustransfer mode (ATM), data packets of a fixed length, what are referredto as ATM cells, are used for the data transport. An ATM cell iscomposed of a five byte long cell header—what is referred to as theheader—containing switching data relevant for the transport of an ATMcell and of a 48 byte long payload cell, what is referred to as thepayload. ATM cells transmitted via the virtual connections essentiallycomprise switching data composed of a VPI value and a VCI value in thecell header. The data deposited in the header are processed at the inputof an ATM network node, i.e. the switching data arranged therein areacquired and interpreted. Subsequently, the ATM cells are switched to anoutput representing a specific destination on the basis of the switchinginformation stored in the connection table, being switched thereto by aswitching network module arranged in the ATM network node.

In order to be able to emulate connectionless services in an ATM-basedcommunication network, a conversion of the switching data deposited inthe cell header of a communicated ATM cell must ensue in every ATMnetwork node arranged in the ATM-based communication network, so thatthe required switching capacity or, calculating performance increasesgreatly in an ATM network node. Given an increased data volume, this canlead to a communication delay—often referred to as “delay” in theliterature—, so that, for example, connectionless services cannot beutilized within the scope of applications having real-time demands.

In order to reduce the required calculating outlay in an ATM networknode, “ATM networks—concepts, protocols, applications”, Addison-Wesley,3^(rd) edition, 1998, ISBN 0-201-17817-6 discloses that connectionlessservices be realized via specific, what are referred to as “CL servers”({overscore (C)}onnection {overscore (L)}ess {overscore (S)}erver).These CL servers are connected to one another and undertake the addressconversions needed for an emulation of connectionless services in anATM-base communication network analogous to the methods that areimplemented in routers. Given the methods employed here, however, aprocessing or, communication delay can also arise given an elevated datavolume.

SUMMARY OF THE INVENTION

The present invention is based on the object of specifying a methodwherein the processing or, communication delay is reduced in anemulation of connectionless services via a connection-orientedcommunication network.

This object is inventively achieved by communicating a connection setupmessage that includes a destination address and a source address to anetwork node. The network node enters its address into the connectionsetup message. The connection setup message is then forwarded via thenetwork node that receives the connection set up message to aneighboring network node. Upon reception of the connection set upmessage at a destination node the connection setup message is forwardedto a destination communication terminal device. A confirmation messageis then returned to the source communication terminal device andswitching information for messages to be subsequently transmittedbetween the source communication terminal and the destinationcommunication terminal device are deposited in network nodes that aretraversed.

A critical advantage of the invention is that, in contrast to the priorart wherein switching information for all network nodes arranged in thecommunication network are stored in a network node in the presentinvention, only those switching information are stored in the networknodes of the communication network that are required for the connectionscurrently conducted over the network node. This leads to a considerablereduction of the memory capacity required in the network node.

Another advantage of the invention is that, given the present method forroute determination and in contrast to the signaling in aconnection-oriented communication network, no transmission conditionssuch as, for example, a declaration about the required transmissioncapacity or about real-time demands are made, so that a routedetermination and a subsequent message communication can be realizedfaster.

In another embodiment of the of the invention wherein a connection setupmessage or, a confirmation message is not forwarded up to theoriginating or, destination communication terminal device participatingin a connection but is processed in the network node allocated to theoriginating or, destination communication terminal device. This has theadvantage that the source or, the destination communication terminaldevice can be kept free of routing jobs.

One other advantage of developments of the invention is that a decisionabout the selection of a route between a source communication terminaldevice and a destination communication terminal device can be made bythe subscriber at the destination communication terminal device, so thatthe criteria for a connection setup relevant to said subscriber such as,for example, the transmission time, the costs or the transmissioncapacity made available on the identified route take effect.

As a result of a deletion of switching information stored in a networknode after expiration of a prescribable time span (for example, after 10minutes) wherein no messages allocated to these switching informationwere communicated, assures that only the currently acquired switchinginformation are stored in a network node.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a structogram directed to the schematic illustration of anATM-based communication network with network nodes arranged therein;

FIG. 2 shows a structogram directed to the schematic illustration of aconnection setup message or, respectively, a confirmation message;

FIG. 3 shows a flow chart for illustrating the method steps sequencingin a communication of a connection setup message from a sourcecommunication terminal device to a destination communication terminaldevice;

FIG. 4 shows a flow chart for illustrating the method steps sequencinggiven a communication of a confirmation message from the destinationcommunication terminal device to the source communication terminaldevice.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG 1. shows a schematic illustration of an ATM-based communicationnetwork ATM-KN having network nodes NK arranged therein and connected toone another. FIG. 1 shows five network nodes, NK1 through NK5. Thenetwork nodes NK are realized, for example, by ATM switching systems towhich communication terminal devices can be connected. By way ofexample, two communication terminal devices KE are shown that areconnected via a fourth network node NK4 or, respectively, via a fifthnetwork node NK5 to the ATM-based communication network ATM-KN.

Further, a source communication terminal device U-KE is connected to theATM-based communication network ATM-KS via a network node NK—referred toas source network node UNK below—and a destination communicationterminal device Z-KE is connected to the ATM-based communication networkATM-KN via a further network node NK—referred to below as destinationnetwork node ZNK.

Proceeding from the source communication terminal device U-KE, a messageis to be communicated to the destination communication terminal devicesZ-KE via the ATM-based communication network ATM-KN.

To this end, a connection setup message R is communicate d from thesource communication terminal device U-KE to the source network node UNKfor a determination of a route from the source communication terminaldevice U-KE to the destination communication device Z-KE. The individualnetwork nodes NK are connected to one another via a specific connectionfor the communication of connection setup messages are to a neighboringnetwork node NK. For example, a specific transmission channel—frequentlyabbreviated in the literature as VC ({overscore (V)}irtual {overscore(C)}hannel)—is reserved for the communication of connection setupmessages R. A connection setup message R can be communicated to thedestination communication terminal devices ZK-E from the sourcecommunication terminal device U-KE via various routes LW. For example, afirst route LW1 and a second route LW2 are shown with broken lines inthe Figure.

FIG. 2 shows a schematic illustration of a connection setup message R({overscore (R)}equest) or, of a confirmation message E (Ēstablished).The connection setup message R or, the confirmation message E iscomposed of a layer-2 destination address field L2-DA ({overscore(L)}ayer 2—{overscore (D)}estination Āddress), of a layer-2 sourceaddress field L2-SA ({overscore (L)}ayer 2—{overscore (S)}ource Āddress)and of a service data field L2-SDU ({overscore (L)}ayer 2—{overscore(S)}ervice {overscore (D)}ata Ūnit). In the present example, the layer-2destination address field L2-DA contains the layer-2 address L2-Z-KEaccording to the OSI reference model of the destination communicationterminal device Z-KE and the layer-2 source address field L2-SA containsthe layer-2 address L2-U-KE according to the OSI reference model of thesource communication terminal device U-KE.

The service data field L2-SDU is subdivided into a layer-3 destinationaddress field L3-DA, into a layer-3 source address field L3-SA, into aprotocol info-field PI and into n address pair fields 1.HOP AP, . . .,n.HOP AP. In the present example, the layer-3 destination address fieldL3-DA contains the layer-3 address L3Z-KE according to the OSI referencemodel of the destination communication terminal device Z-KE, and thelayer-3 source address field L3-SA contains the layer-3 address L3-U-KEaccording to the OSI reference model of the source communicationterminal device U-KE.

The protocol info-field PI serves to distinguish between connectionsetup message R and confirmation message E and alternatively contains an“R” or an “E” as entry. When the protocol info-field PI exhibits an “R”as entry, then it is a matter of a connection setup message R. When theprotocol info-field PI exhibits an “E” as entry, then it is a matter ofa confirmation message B.

The address pair fields 1.HOP AP, . . . ,n.HOP AP are respectivelysubdivided into a layer-3 address field L3-AF and into a layer-2 addressfield L2-AF. The layer-3 address is L3-NK are stored in the addressfield pairs 1.HOP AP, . . . ,n.HOP AP in the layer-3 address field L3-AFand the layer-2 addresses L2-NK of the network nodes NK traversed on aroute LW are stored therein in the layer-2 address field L2-AF.

A connection setup message R communicated via the first route LW1 fromthe source communication terminal device U-KE to the destinationcommunication terminal device Z-KE contains three valid address pairfields 1.HOP AP, . . . ,3.HOP AP. The first address pair field 1.HOP APcontains the layer-3 address L3-UNK of the source network node UNK. Thesecond address pair field 2.HOP AP contains the slice-3 address L3-NK3of the third network node NK3. The third address pair field 3.HOP APcontains the layer-3 address L3-ZNK of the destination network node ZNK.

A connection setup message R communicated via the second route LW2 fromthe source communication terminal device U-KE to the destinationcommunication terminal device Z-KE contains five valid address pairfields 1.HOP AP, . . . ,5.HOP AP. The first address pair field 1.HOP APcontains the layer-3 address L3-UNK of the source network node UNK. Thesecond, third and fourth address pair field 2.HOP AP, 3.HOP AP, 4.HOP APcontain the layer-3 addresses L3-NK4, L35 NKS, L3-NK3 of the fourth,fifth and third network node NK4, NK5, NK3. The fifth address pair field5.HOP AP contains the layer-3 address L3-ZNK of the destination networknode ZNK.

FIG. 3 shows a flow chart for illustrating the method steps sequencingin a communication of a connection setup message R from the sourcecommunication terminal device U-KE to the destination communicationterminal device Z-NKE.

When, proceeding from the source communication terminal device U-KE, amessage is to be communicated to the destination communication terminaldevice Z-KE, then the source communication terminal device U-KE sends aconnection setup message R to the source network node UNK via thepre-defined transmission channel. The network node NK receiving aconnection setup message R interprets the destination address L3-Z-KE ofthe destination communication terminal device Z-KE deposited in thelayer-3 destination address field L3-DA and enters the layer-3 addressL3-NK allocated to it in the ATM-based communication network ATM-KN inthe layer-3 address field L3-AF of the first free address pair field1.HOP AP, . . . n.HOP AP. When the network node NK is the source networknode UNK, then the source network node UNK enters the layer-3 addressL3-UNK in the layer-3 address field L3-AF of the first address pairfield 1 .HOP AP.

In a next step, a check is carried out to see whether the network nodeNK that has received a connection setup message R, is the destinationnetwork node ZNK. When this is the case, the connection setup message Ris communicated directly to the destination communication terminaldevice Z-KE via the pre-defined transmission channel. The method stepssequencing in this case are explained in greater detail with referenceto FIG. 4. When the network node NK is not the destination network nodeZNK, then a check is carried out to see whether the destination addressL3-Z-KE of the destination communication terminal device Z-KE depositedin the layer-3 destination address field L3-DA is known in the networknode NK. When this is the case, then the connection setup message R isforwarded via the pre-defined transmission channel to the next networknode NK lying on the direct route to the destination network node ZNK.

When the destination address L3-Z-KE is not known in the network nodeNK, then the connection setup message R is forwarded via the pre-definedtransmission channels to all neighboring network nodes NK whose layer-3addresses L3-NK are not entered in a layer-3 address field L3-AF of anaddress pair field 1.HOP AP, . . . , n.HOP AP. This measure preventsloop formations from occurring in the determination of a route LW.

Before a transmission of the connection setup message R to a furthernetwork node NK, the plurality of network nodes NK previously traversedby the connection setup message R is determined, i.e. the plurality ofentries in a layer-3 address field L3-AF of the address pair field s1.HOP AP, . . . ,n.HOP AP. When the plurality has reached an adjustablelimit value, then the connection setup message R is discarded. Thismeasure assures that the transmission resources made available by theATM-based communication network ATM-KN are not unnecessarily occupied inthe determination of a route LW.

FIG. 4 shows a flow chart for illustrating the method steps sequencinggiven a transmission of a confirmation message E from the destinationcommunication terminal device Z-KE to the source communication terminaldevice U-KE. When the destination communication terminal Z-KE hasreceived a plurality of connection setup messages R within aprescribable time span, a connection setup message R is selectedaccording to prescribable criteria. For example, the transmissionduration of a connection setup message R, the number of network nodes NKtraversed on the route LW defined by the connection setup message R, thecosts incurred due to the route LW or the transmission capacity madeavailable on the route LW are selected as criteria for the selection fora connection setup message R. Alternatively, combinations of thesecriteria can also be utilized for the selection of a connection setupmessage R.

After the selection of a connection setup message R, the otherconnection setup messages R are discarded and the selected connectionsetup message R is converted into a confirmation message E by modifyingthe entry in the protocol infofield PR from “R” to “E”.

In a next step, the layer-3 address L3-NK is interpreted in the layer-3address field L3-AF of the n.address pair field n.HOP AP, and thelayer-2 address L2-NK of the network node NK referenced by this addressis entered in the layer-2 address field L2-AF of the n.address pairfield n.HOP AP. In this case, the network node NK is the destinationnetwork node ZNK. Subsequently, the confirmation message E, proceedingfrom the destination communication terminal device Z-KE via thepre-defined transmission channel, is communicated to the network nodeNK—the destination network node ZNK in this case—referenced by thelayer-3 address L3-NK deposited in the layer-3 address field L3-AF ofthe n.address pair field n.HOP AP. A switching information is stored inthe network node NK for a following message communication between thesource communication terminal device UK-KE and the destinationcommunication terminal device Z-KE. This switching information composedof an input VCI value and an output VCI value indicates which inputchannel is connected to which output channel of the network node inswitching-oriented terms.

When the network node NK is a matter of the source network UNK, i.e.when n=1, then the confirmation message is forwarded via the predefinedtransmission channel directly to the source communication terminaldevice U-KE.

When the network node NK is not the source network node UNK, the layer-3address L3-NK in the layer-3 address field L3-AF of the n-first addresspair field n-1.HOP AP is interpreted in a next step, and the slice-2address L2-NK of the network node NK referenced by this address isentered in the layer-2 address field L2-AF of the n-1.address pair fieldn-1.HOP AP. Subsequently, the confirmation message E is communicated viathe predefined transmission channel to the network node NK referenced bythe layer-3 address L3-NK deposited in the layer-3 address field L3-AFof the n-1 address pair field n-1.HOP AP, and the switching informationneeded for a subsequent message communication between the sourcecommunication terminal device U-KE and the destination communicationterminal device Z-KE and composed of input VCI value and output VCIvalue is stored.

These method steps are repeated until the confirmation message E reachesthe source network node UNK, proceeding from which it is communicatedvia the predefined transmission channel to the source communicationterminal device U-KE.

When, given the present exemplary embodiment, for example, the pluralityn of network nodes NK traversed on a route LW forms the basis ascriterion for a selection of a connection setup message R at thedestination communication terminal equipment Z-KE, then the connectionsetup message R representing the first route LW1 is selected andconverted into a confirmation message E. The connection setup message Rrepresenting the second route LW2 is discarded.

The layer-3 address L3-ZNK in the layer-3 address field L3-AF of thethird address pair field 3.HOP AP is interpreted in the destinationcommunication terminal device Z-KE, and the layer-2 address L2-ZNK ofthe destination network node ZNK indicated by the layer-3 address L3-ZNKis entered in the layer-2 address field L2-AF of the third address pairfield 3.HOP AP. Subsequently, the confirmation message E is communicatedproceeding from the destination communication terminal device ZKE viathe predefined transmission channel to the destination network node ZNK.The switching information composed of input VCI value and output VICvalue that is relevant for a subsequent message transmission is storedin the destination network node. In a next step, the layer-3 addressL3-NK3 in the layer-3 address field N3-AF of the second address pairfield 2.HOP AP is interpreted, and the layer-2 address L2-NK3 of thethird network node NK3 referenced by the layer-3 address L3-NK3 isentered in the layer-2 address field L2-AF of the second address pairfield 2.HOP AP. Subsequently, the confirmation message E is communicatedto the third network node NK3 via the predefined transmission channelproceeding from the destination network node Z-NK, the switchinginformation relevant for a subsequent message communication being storedin said third network node NK3. In a further step, the layer-3 addressL3-UNK in the layer-3 address field L3-AF of the first address pairfield 1.HOP AP is interpreted, and the layer-2 address L2-UNK of thesource network node UNK referenced by the layer-3 address L3-UNK isentered in the layer-2 address field L2-AF of the first address pairfield 1.HOP AP. Subsequently, the confirmation message E is communicatedto the source network node NK3 via the predefined transmission channelproceeding from the third network node NK3, the switching informationrelevant for a subsequent message communication being stored in saidsource network node NK3. In a final step, the confirmation message E iscommunicated via the predefined transmission channel to the sourcecommunication terminal device U-KE.

When no messages are communicated via the connection between the sourcecommunication terminal device U-KE and the destination communicationterminal device Z-KE allocated to the switching information stored in anetwork node NK within an adjustable time span, for example with a timespan of 10 minutes, then this switching information is deleted. It isthus assured that the switching information stored in a network node NKare constantly updated.

In contrast to the traditional signaling in an ATM-based communicationnetwork ATM-KN, wherein switching information for a message transmissionto a further network node NK arranged in the ATM-based communicationnetwork ATM-KN must be stored in every switching node NK, only thoseswitching information that are required for the connections currentlyconducted across the network node NK are stored in a network node NKgiven the disclosed method for route determination.

This leads to a considerable reduction of the required address memorycapacity in the network node NK and to an increase in the switchingspeed.

In contrast to the traditional signaling or in the route LW between thesource communication terminal device U-KE and the destinationcommunication terminal device Z-KE is predetermined by switchinginformation stored in the source network node UNK, further, a selectionof a route LW between the source communication terminal device U-KE andthe destination communication terminal device Z-KE is undertaken by thesubscriber at the destination communication terminal device Z-KE. Thus,criteria for a connection setup such as, for example, the transmissiontime, the costs incurred by a route LW or the transmission capacity madeavailable on a route LW that are relevant for the subscriber can thus betaken into consideration situation-condition.

In the present method for route determination and in contras to thetraditional signaling in an ATM-based communication network ATM-KN, notransmission conditions such as, for example, a decoration about thetransmission capacity required or about real-time demands are made. As aresult thereof, a route determination and a subsequent messagetransmission between the source communication terminal device U-KE andthe destination communication terminal device Z-KE can be realizedfaster. The communication of a connection setup message R or, of aconfirmation message E in the ATM-based communication network ATM-KNensues with the available transmission bit rate—frequently abbreviatedas ABR (Āvailable {overscore (B)}itrate) in the literature. As a resultof the inventive method, thus, only processing delay or, transmissiondelayed as in the scope of connection-oriented services arise given anemulation of connectionless services via the ATM-based communicationnetwork ATM-KN.

Although other modifications and changes may be suggested by thoseskilled in the art, it is the intention of the inventors to embodywithin the patent warranted hereon all changes and modifications asreasonably and properly come within the scope of their contribution tothe art.

1. A method for establishing a route via a connection-orientedcommunication network with a plurality of network nodes connected to oneanother for emulating connectionless services, comprising the steps of:communicating a connection setup message including a destination addressand a source address to a network node, said connection setup messageproceeding from a source communication terminal device; entering anetwork address into the connection setup message via said network node,said network address being allocated to the network node in thecommunication network; forwarding the connection setup message via thenetwork node that receives the connection setup message to at least oneneighboring network node; forwarding the connection setup message to adestination communication terminal device upon reception of theconnection setup message at a destination node, said destination nodebeing identifiable with an assistance of the destination address; andreturning a confirmation message to the source communication terminaldevice on said route, said route being defined by the source address,said route also being defined by the network node address, a switchinginformation for messages to be subsequently transmitted between thesource communication terminal and the destination communication terminaldevice being deposited in network nodes that are traversed, wherein thenetwork node receiving the connection setup message forwards theconnection setup message to one or more other network nodes only if theonly one or more other network nodes each has a network node address notentered in the received connection setup message, the one or more othernetwork nodes being connected to the network node receiving theconnection setup message.
 2. A method for establishing a route via aconnection-oriented communication network with a plurality of networknodes connected to one another for emulating connectionless services,comprising the steps of: communicating a connection setup messageincluding a destination address and a source address to a network node,said connection setup message proceeding from a source communicationterminal device; entering a network address into the connection setupmessage via said network node, said network address being allocated tothe network node in the communication network; forwarding the connectionsetup message via the network node that receives the connection setupmessage to at least one neighboring network node; and returning aconfirmation message to the source communication terminal device on saidroute upon receiving of the connection setup message at a destinationnode, said destination node identifiable with an assistance of thedestination address, said route being defined by the source address,said route also being defined by the network node address, a switchinginformation for messages to be subsequently transmitted between thesource communication terminal and the destination communication terminaldevice being deposited in network nodes that are traversed, wherein thenetwork node receiving the connection setup message forwards theconnection setup message to one or more other network nodes only if theonly one or more other network nodes each has a network node address notentered in the received connection setup message, the one or more othernetwork nodes being connected to the network node receiving theconnection setup message.
 3. A method for establishing a route via aconnection-oriented communication network with a plurality of networknodes connected to one another for emulating connectionless services,comprising the steps of: communicating a connection setup messageincluding a destination address and a source address to a network node,said connection setup message proceeding from a source communicationterminal device; entering a network address into the connection setupmessage via said network node, said network address being allocated tothe network node in the communication network; forwarding the connectionsetup message via the network node that receives the connection setupmessage to at least one neighboring network node; forwarding theconnection setup message to a destination communication terminal deviceupon reception of the connection setup message at a destination node,said destination node being identifiable with an assistance of thedestination address; and returning a confirmation message to a sourcenetwork node to which the source communication terminal device isallocated on said route, said route being defined by the source address,said route also being defined by the network node address, a switchinginformation for messages to be subsequently transmitted between thesource communication terminal and the destination communication terminaldevice being deposited in network nodes that are traversed, wherein thenetwork node receiving the connection setup message forwards theconnection setup message to one or more other network nodes only if theonly one or more other network nodes each has a network node address notentered in the received connection setup message, the one or more othernetwork nodes being connected to the network node receiving theconnection setup message.
 4. A method for establishing a route via aconnection-oriented communication network with a plurality of networknodes connected to one another for emulating connectionless services,comprising the steps of: communicating a connection setup messageincluding a destination address and a source address to a network node,said connection setup message proceeding from a source communicationterminal device; entering a network address into the connection setupmessage via said network node, said network address being allocated tothe network node in the communication network; forwarding the connectionsetup message via the network node that receives the connection setupmessage to at least one neighboring network node; and returning aconfirmation message to a source network node on said route uponreceiving of the connection setup message at a destination node, saiddestination node identifiable with an assistance of the destinationaddress, said route being defined by the source address, said mute alsobeing defined by the network node address, said source communicationterminal device being allocated to said source network node, a switchinginformation for messages to be subsequently transmitted between thesource communication terminal and the destination communication terminaldevice being deposited in network nodes that are traversed, wherein thenetwork node receiving the connection setup message forwards theconnection setup message to one or more other network nodes only if theonly one or more other network nodes each has network node address notentered in the received connection setup message, the one or more othernetwork nodes being connected to the network node receiving theconnection setup message.
 5. A method according to claim 1, furthercomprising the step of: communicating the connection setup message to asource network node, said source communication terminal device beingconnected to the communication network via said source network node. 6.A method according to claim 1, wherein said network node receiving theconnection setup message forwards the connection setup message tonetwork nodes being connected to the network node receiving theconnection only when a plurality of network nodes traversed by areceived connection setup message is lower than an adjustable limitvalue.
 7. A method according to claim 1, wherein in instances where aplurality of connection setup messages are received at the destinationcommunication terminal device, further comprising the steps of:selecting one of received connection setup messages based on apredetermined criteria; and returning said confirmation message only fora setup message selected based on said selecting step.
 8. A methodaccording to claim 7, wherein only connection setup messages that arrivewithin a predetermined time span after reception of a first connectionsetup message at the destination communication terminal device areconsidered for said selecting step.
 9. A method according to claim 7,wherein said predetermined criteria is based on the plurality of thenetwork nodes traversed on said route, said route being defined by theconnection setup message.
 10. A method according to claim 7, whereinsaid predetermined criteria is based on costs incurred on said route,said route being defined by the connection setup message.
 11. A methodaccording to claim 7, wherein said predetermined criteria depends on atransmission capacity made available on said route, said route beingdefined by the connection setup message.
 12. A method according claim 1,wherein a transmission of at least one of the connection setup messageand the confirmation message between neighboring network nodes ensuesvia a specific connection provided exclusively for transmission of atleast one of the connection setup and the confirmation message.
 13. Amethod according to claim 12, wherein at least one channel of aconnecting line between two neighboring network nodes is reserved forsaid specific connection.
 14. A method according to claim 1, wherein ani^(th) network node receiving the connection setup message enters thenetwork node address being allocated to said i^(th) network node in thecommunication network into an address field of an i^(th) address pairfield of the connection setup message.
 15. A method according to claim14, wherein the network node address is the layer-3 address of thenetwork node according to Open Systems interconnection reference model.16. A method according to claim 14, wherein the i^(th) network nodereceiving the confirmation message enters a layer-2 address into afurther address field of the i^(th) address pair field of theconfirmation message, said layer-2 address being allocated to saidi^(th) network node communication network according to the Open Systemsinterconnection reference model.
 17. A method according to claim 1,wherein for a bi-directional message communication between the sourcecommunication terminal device and the destination communication terminaldevice the switching information being deposited sets which input of thenetwork node is linked to which output of the network node.
 18. A methodaccording to claim 17, wherein the switching information is deletedafter a predetermined time span in which no messages were transmittedbetween the source communication terminal device and the destinationcommunication terminal device.